The present invention relates generally to an optical information record/read apparatus with which an optical information can be recorded on and/or read out from an optical record medium and which is generally called an optical pickup. More particularly, the invention relates to an optical information record/read apparatus which employs an optical waveguide element.
An optical information record/read apparatus employing an optical waveguide element has been proposed. The use of such an optical waveguide element can make it possible to fabricate a small-sized and light-weight optical information record/read apparatus. Therefore, recently, it has been attempted to put into practice an optical information record/read apparatus employing an optical waveguide element.
Generally, an optical waveguide element for use in an optical information record/read apparatus comprises a waveguide layer formed on a transparent substrate. The waveguide layer is provided with a light coupling means for coupling the light beam reflected from the optical record medium with the waveguide layer so that the light beam coupled with the waveguide layer is then propagated through the waveguide layer as a guided light beam. The waveguide layer is further provided with a light detecting system for detecting the guided light beam, and a waveguide reflection optical system for leading the guided light beam, propagated through the waveguide layer, toward the light detecting system while converging the same.
The use of a waveguide lens as a waveguide optical system, such as mode index lens, Luneburg lens, geodesic lens or grating lens, which are described in OYOBUTURI, Japan Society of Applied Physics, Vol. 48, No. 3, p. 241 et seq., 1979, has been proposed. These waveguide lenses, however, make it difficult to put into practice the optical information record/read apparatus having the waveguide element, due to the following reason.
In the fabricating process of the mode index lens or the Luneburg lens, it is necessary to control the refractive index thereof with extremely high accuracy. However, with the present techniques, it is generally difficult to perform such control with extremely high accuracy. Accordingly, in the present stage, it is difficult, in view of mass production, to put into practice the optical waveguide element having the mode index lens or Luneburg lens.
The geodesic lens is made by forming a depression having a non-spherical inner surface on the surface of the waveguide layer. Machining of such a non-spherical depression is generally difficult and thus requires precise grinding and subsequent polishing processes. Accordingly, the use of the geodesic lens makes it difficult to mass-produce the waveguide optical system, resulting in an increase of manufacturing cost.
On the other hand, the grating lens can be relatively easily fabricated with low manufacturing cost. However, the grating lens has a characteristic in that the lens action thereof depends on the wave length of light such that the focal length thereof varies with the wave length of light. With respect to this, an ordinary semiconductor laser, which is widely used as a light source of an optical information record/read apparatus, has a characteristic in that the wave length of laser beam produced thereby varies with temperature. Accordingly, when using the grating lens as a waveguide optical system, it is necessary to perform temperature control for the ordinary semiconductor laser with high accuracy or necessary to use a semiconductor laser of a distributed feedback (DFB) type in which the shift of wave length of laser beam does not occur, resulting in an increase in the size of optical information record/read apparatus and an increase in the manufacturing cost thereof.